Apparatus and method for diathermy treatment and control

ABSTRACT

A method for therapeutic deep heating of musculoskeletal tissues with an improved transducer that serves simultaneously to couple the power from the generator into the patient and to sense the therapeutic response for treatment control including a method of manufacture and testing of contact applicators for dielectric heating of musculoskeletal tissue. The applicator is comprised of rectangular wave guide in which dielectric material is placed to reduce the guide wave length to the free-space value at the frequency of operation. In addition, the invention comprises a method and apparatus for the noninvasive detection of therapeutic response in muscle tissue to dielectric heating. Ths response is then used to control the treatment. Both heating and sensing are accomplished by one transducer and one apparatus if dielectric heating is employed. If other forms of heating are used, such as ultrasound, the sensor still occurs but the apparatus must be modified, the modifications including replacement of the high power electromagnetic source with a low power source version.

PATENT DOCUMENTS AND PUBLICATIONS

U.S. Pat. No. 2,407,690, Southworth, 9/1946

U.S. Pat. No. 3,065,752, Potzl, 11/1962

U.S. Pat. No. 4,108,147, Kantor, 8/1978

U.S. Pat. No. 4,138,998, Nowogrodzki, 2/1979

U.S. Pat. No. 4,312,364, Convert, 1/1982

U.S. Pat. No. 4,341,227, Turner, 6/1982

U.S. Pat. No. 4,346,716, Carr, 8/1982

U.S. Pat. No. 4,409,993, Furihata, 10/1983

U.S. Pat. No. 4,446,874, Vaguine, 5/1984

U.S. Pat. No. 4,557,272, Carr, 12/1985

Cheung, A. Y., Dao, T., Robinson, J. E., Radio Science 12: 81-85, 1977.

VanKoughnett, A. l. and Wyslouzil, Journal of Microwave Power, 7:381-383, 1972.

Heeren, R. G. and Baird, J. R., IEEE Transactions on Microwave Theoryand Technique, MTT-15: 415-421, 1971.

Hudson, A. C., IRE Transactions on Microwave Theory and Technique, April1957, MTT-5: 161-162.

Moreno, T., Microwave Transmission Design Data, Chapter 11 WaveguidesFilled with Dielectric materials, Dover, N.Y., 1958; reproduction ofSperry Gyroscope Co report of the same title, copyright 1948.

Frank, N. H., [Wave Guide Handbook, Section V, Dielectric Structures inWaveguide, Report T-9, Section I. Radiation Laboratory, Mass. Instituteof Technology, 1942.

FIELD OF THE INVENTION

This invention relates to a transducer and apparatus for deep heattherapy in the treatment of musculoskeletal disorders, and moreparticularly to low leakage radio frequency (RF) contact applicatordesign with skin and subcutaneous cooling, applicator manufacturing,including applicator testing for quality assurance, and for detection oftherapeutic response to achieve treatment control that may use the sametransducer simultaneously for effector and sensor functions.

BACKGROUND OF THE INVENTION

That dielectric heating of musculoskeletal tissue is more efficaciousand more efficiently accomplished by contact applicators was establishedby Kantor, U.S. Pat. No. 4,108,147.

Subsequent improvements deal with broad band tuning to accomplishefficient transfer of microwave energy from applicator into tissue overa wide band of frequencies, and cooling using air as well as water, orconvective as well as conductive.

A slotted, metallic cover over the radiating aperature of a waveguideapplicator was the subject of the Potzl patent, U.S. Pat. No. 3,065,752.

Vaguine in U.S. Pat. No. 4,446,874 made claims concerning coupling andtuning involving discoupling input coupling of the magnetic loop wherebythe frequency of operation and input match are adjusted.

The design procedures cited in the referenced patents were not viablebecause these procedures did not provide for compensation and control ofevanescent modes in the waveguide applicator. These modes existprincipally in the area of the feed that couples microwave energy fromthe generator via a coaxial cable into the applicator, and on into thepatient.

As a result of these modes, the guide wavelength is not equal to thefree space wavelength at the frequency of operation, i.e., the TEM modereferred to by Kantor in U.S. Pat. No. 4,108,147 is not necessarilyestablished. The TEM mode cannot exist in a hollow tube waveguide,nevertheless, uniformity of the electric field across the aperture canbe improved when the guide wave length is shortened to that of the freespace by the use of partial filling with dielectric material parallel tothe narrow wall of the guide.

The reduction of guide wavelength to the free space value is, therefore,a necessary, but not a sufficient condition to accomplish more nearlyuniform electric fields across the aperture. Although the guidewavelength may also be shortened by partial filling by dielectricparallel to the broad wall, this does not yield the uniform electricfield distribution across the aperture.

The instant invention shows that the length of the dielectric materialin the waveguide applicator must also be an appreciable fraction of awavelength in order to establish the desired guide wavelength andprovides for confirmation of the guide wavelength and methods of qualityassurance; no methods for confirmation of the guide wavelength or forquality assurance exist in the prior art.

Additionally, this invention establishes the relationship betweenaperture electric field distribution, guide wavelength, and specificabsorption rates at depth sites, none of which is provided for by theprior art.

The instant invention also improves air cooling methods of prior designswhich were non-contacting in order to allow egress of air over thepatient's skin. The necessary spacing promoted RF leakage as well astuning variation as the air gap varied with breathing or other motions.RF leakage was not controlled at the point of air ingress and the simplepropeller fan mounted within the applicator of the prior designintroduces undesirable vibration that modulates the match by alterationof the air gap.

The invention provides for detection of therapeutic response to controldielectric heating during the treatment. Until this invention, nospecific individual treatment response has been possible. Prior art wassubjective, and at best, the manufacturer provided tabled standards ofpower and duration for the general population which failed to accomodatefor the variations between individuals and were no more than generalrecommendations. The instant invention makes use of the increase inlocal blood flow in muscle consequent to local temperature elevation andwave impedance change due to the change in tissue electrical properties,i.e., the instant invention both provokes and detects reactive hyperemiawhich is the therapeutic response.

The technology of combined microwave heating with sensing has beenrecognized in other areas. The Furihata patent, U.S. Pat. No. 4,409,993addressed the need to control dose in an endoscopic device that usesmicrowave power to heat cancerous tissue to the point of eschar asverified by optical visualization of necrosis. The Converse patent, U.S.Pat. No. 4,312,364, and its progeny, the Carr patents, U.S. Pat. Nos.4,346,716 and 4,557,272, use microwave radiometry to sense heating froman exogenous microwave source.

The instant invention uniquely provides for both heating and sensing ofthe therapeutic response through the dual use of an antenna. No priorart utilizes the combined effector/sensor action of the instantinvention, using the change in complex permittivity of the target tissuedue to local vasodilation, nor were the prior methods based on a closelycoupled antenna whereby antenna impedance alterations are used to inferchanges in the wave impedance of the tissue secondary to the desiredreactive hyperemia. Prior technology did not use the critical guidewavelength, design methods, a radome, or surface cooling incorporated aswith the instant invention.

SUMMARY OF THE INVENTION

This invention provides new, improved treatment apparatus for dielectricheating as a therapy for musculoskeletal disorders. Implemented areimproved methods for contact applicator design which produce more nearlyuniform heating in the transverse plane, greater depth of microwavepenetration, and apparatus construction which can utilize a dual role ofthe transducer for both application of power as well as a transducer forsensing the therapeutic response during the treatment withoutinterruption of power delivery.

Quality assurance provisions include guide wavelength verification,input match as a function of frequency as well as guide wavelength, andair cooling of the skin which has eliminated spaced applicators and doesnot promote RF leakage.

A thin radome with a dielectric constant approximately that ofsubcutaneous fat is employed to interface the applicator to the patient.The radome serves to both prevent fringe field coupling to the patient(leading to excessive heating at the narrow walls of the wave guidewhere they would otherwise contact the patient), and to provide a lowthermal impedance between the air cooling that is applied on its innersurface and the patient's skin that is in contact with its outersurface.

The invention provides for use of the applicator additionally as asensor for detection of therapeutic response, and use of the sensorresponse to control the dielectric heating treatment on an individualbasis. This is accomplished by measurement and control of the net powerabsorbed at a level sufficient to produce the desired therapeuticresponse of increased muscle blood flow. The increased muscle blood flowis a reactive hyperemia in response to temperature elevation. Localtemperature elevation in the muscle provokes local vasodilation, openingcapillary beds and arterioles. The desired therapeutic response is thisreactive hyperemia, i.e., increased local blood flow which promotes, forexample, resolution of inflammatory infiltrates. The detection ofreactive hyperemia also provides an indirect and qualitative measure ofmuscle temperature in the pattern of the applicator since the localvascular response is triggered at temperatures near 40 degreescentigrade.

An object of this invention is to provide improved treatment apparatusfor dielectric heating as a therapy for musculoskeletal disorders.

Another object of this invention is to use increased muscle blood flowwhich is reactive hyperemia in response to temperature elevation.

Yet another object is to provide a contact applicator design thatproduces more nearly uniform heating in the transverse plane.

A further object of this invention is an apparatus for treatment whichfacilitates treatment at greater depths of penetration.

Still another object of this invention is to provide apparatus whichacts as both a transducer for application of power, as well as atransducer for sensing the therapeutic response, reactive hyperemia,during the treatment.

Yet another object of this invention is to permit sensing of therapeuticresponses without interruption of power delivery.

A further object of this invention is to provide for optimization of thecritical parameter of guide wavelength and for the quality assurance foreach applicator that includes input match as a function of frequency aswell as actual guide wavelength.

Yet another object of this invention is to provide for air cooling ofthe skin that do not require spaced applicators and do not promote RFleakage.

It is also an object of this invention to employ a thin radome with adielectric constant near that of subcutaneous fat to interface theapplicator to the patient.

It is a further object of the invention to provide a thin radome tointerface the applicator to the patient which prevents fringe fieldcoupling to the patient that normally leads to unwanted heating at thenarrow walls of the wave guide where they would otherwise contact thepatient.

Yet another object of the invention is to provide a thin radome tointerface the applicator to the patient which yields a low thermalimpedance between the air cooling that is applied on its inner surfaceand the skin of the patient that is in contact with its outer surface.

Another object of the invention is to use an applicator as a sensor fordetection of therapeutic response, reactive hyperemia, as a means tocontrol the dielectric heating treatment on an individual basis.

Further objects and advantages of this invention will become moreapparent in light of the following drawings and description of thepreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 are the top, side and end orthographic projections,respectively, of one configuration of a preferred embodiment of theinvention for applicator/sensor showing a monopole type of electricfield feed as the coax to waveguide adapter;

FIGS. 4 and 5 are top and side orthographic projections, respectively,analogous to FIGS. 1 and 2 above, of another embodiment using a magneticfield feed in the form of a shorted loop;

FIGS. 6, 7 and 8 illustrate a high dielectric constant (above criticalvalue), the critical value dielectric constant, and a low dielectricconstant, respectively, in diagrammatic views of the waveguide showingthe expected electric field distribution in the dielectric material andair filled portion of the waveguide;

FIGS. 9 and 10 are a perspective and end projection, respectively, ofone configuration of a preferred embodiment of the invention which isused for manufacturing quality assurance, e.g., to establish the guidewavelength at the critical value;

FIG. 11 is a functional block diagram of the quality assuranceapparatus;

FIGS. 12 and 13 are analogous to FIGS. 1 and 2, respectively, with addedfunctional block detail showing the method and apparatus for gas coolingand the means for suppression of RF leakage;

FIG. 14 shows a schematic functional block diagram of the system for thenoninvasive detection of the therapeutic response, i.e., reactivehyperemia;

FIG. 15 is a block diagram showing changes illustratingnonelectromagnetic heating modalities.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring to the drawings, FIGS. 1, 2 and 3 generally depict a typicalapplicator 18 of length 20, to be substantially equal to one wavelengthat the free space phase velocity, an electric field feed 22, encased ina polystyrene cylinder 24, placed at a distance 26 of one quarter of theguide wavelength (previously established to be equal to the free spacewavelength at the frequency of operation).

The high dielectric constant (k'=10) and low loss (tan delta=0.0002)ceramic (>96%Al 203) material 28 is placed against the narrow walls ofthe waveguide 36 and held by mechanical fasteners 30 to the narrow wall.The access to the mechanical fixation on the inside of the applicator isclosed by a ceramic plug 32 of substantially the same dielectricproperties as material 28, and a thin, e.g. 0.030", radome 34 fabricatedfrom high thermal conductivity material such as Kapton or composite(e.g. Gl0 with a k'=4 and oriented such that the fiber is crosspolarized to the electric field in the waveguide 36).

The input match is tuned by means of the depth of penetration of thecylindrical feed 22 into the waveguide 36. An optional spring loadedinductive post tuning device 21 is placed between the feed 22 and theshort circuit 38.

There is a connector 40 for the coax cable transmission line from thegenerator. Only coarse tuning to a return loss of less than 10 db iseffected by use of the tuning device 21 with the radome 34 of theapplicator being in contact with simulated fat and muscle phantomprepared according to the methods of prior art. A selected gap isproduced by low loss dielectric shims 41.

Provision for tuning the input impedance to the source are also shown inFIGS. 1, 2 and 3. The thickness of the longitudinal dielectric materialis selected to produce a critical guide wavelength in a test fixture.Small adjustments in the guide wavelength are made by the insertion oflow loss shims 41 between the narrow wall and the dielectric to shortenthe guide wavelength.

A second embodiment is shown in FIGS. 4 and 5 which are the top andright side orthographic projection analogous to FIGS. 1 and 2 above. Thelength 20 of the applicator 18 and dielectric material 28 issubstantially one wavelength at the free space phase velocity. The feed42 is a magnetic loop shorted at a quarter guide wavelength 44. It istuned for input impedance by a capacitive shaft 48 and shaft lock 50.

This is preferable to a tuning screw since the shaft lock 50 is a colletand clamp that make more reproducible RF ground than jamb nut and screw.Another degree of tuning is provided by a stub 52 extending from thepost 54. Only coarse tuning to a return loss less than 10 db is effectedby use of the tuning device with simulated fat and muscle against theradome 43.

FIGS. 6, 7, and 8 illustrate the conditions of guide wavelength shorterthan the critical value, that for the critical value (the free spacevalue), and guide wavelength longer than the critical value,respectively and represent the electric field distribution 56 in thetransverse E plane of guide 58. Use of the design procedure from Kantorand/or Turner will result in the condition shown in FIG. 8 where theelectric field peak is outside of the dielectric material and in the airfilled region of the guide. The critical condition shown in FIG. 7 isalso the one where specific absorbtion rates (SAR) are highest atdistances in the order of 1 to 3 cm below the fat-muscle interface.

The dielectric material 28 is shown in apposition to the narrow wall ofthe applicator 18 and of equal thickness, but of three values ofdielectric constant (high, critical and low) for purposes ofillustration.

The electric field distribution 56 in the transverse plane is effectedby the guide wavelength as the latter relates to the critical value.When the dielectric material 28 decreases the phase velocityexcessively, in comparison to a guide completely filled with air, it mayproduce a guide wavelength that is too short and the electric field peakexists inside the dielectric as shown in FIG. 6. If the dielectricmaterial 28 does not sufficiently contact the guide wavelength, i.e.,the guide wavelength is too long, then the peak occurs in the air filledportion of the guide as shown in FIG. 8. At the critical guidewavelength, the peak is just inside the dielectric at the air interfaceas shown in FIG. 7.

A third embodiment is shown in FIGS. 9 and 10 which is the apparatusused with the method for assuring manufacturing quality and optimizingapplicator operation. This is composed of a waveguide applicator oftwice normal length, shorted at both ends to establish a standing wave,and with a movable carriage/probe to sample the electric fielddistribution via a narrow slot in the center of the guide as shown inFIG. 9. The test fixture guide is of dimensions equal to the applicatorand contains the feed and dielectric material as shown in either of thefirst two preferred embodiments. The electric field feed, for example,and carriage are shown in cross section in FIG. 10. The instrumentationblock diagram shown in FIG. 11 illustrates typical results as well asthe selected node-to-node distance.

FIG. 9 shows a test fixture 58 of length 60, twice the length of theapplicator, with a narrow slot 62, milled into one broad wall. The testfixture 58 is fitted with dielectric of the same thickness andconstitutive properties as that used in the applicator.

The waveguide test fixture interior dimensions are also identical to theapplicator 18 in the transverse plane. The feed is placed at the shortedproximal end 64 whereas the distal end 66 is shorted to produce anelectric standing wave pattern as shown in FIG. 11. The standing wavepattern is measured by a carriage assembly 68 that is scanned along atrack 70 on either side of the slot 62.

The carriage assembly 68 holds a probe 72 connected to a variable linestretcher 74 and thence to a crystal diode detector 76. The carriageruns on the two piece track 70 by means of conductive wheels 78 andspring contacts 80. This permits scanning the probe 72, at anadjustable, but minimal penetration, over a large fraction of the lengthof the test fixture 58.

FIG. 11 shows a signal source 81, a low pass filter 82, with a cut-off10% above the frequency of operation, and the test fixture 58 shownschematically. The feed energized in the test fixture 58 is alsoidentical to that used in the applicator 18. The RF drive produced bythe signal source 81 is square wave modulated at an audio frequency andthe detector output is amplified by a tuned amplifier 86.

A typial pattern of electric field standing waves is shown as a functionof distance from the shorting plate 64 at the feed end. The first nullof the test fixture 58 is 90, the second null is 92, and so on to thelast null 98 at the distal shorting plate 66. The distance between null92, and null 94 is used to estimate half the guide wavelength as itwould exist in the applicator 18.

Additional null-to-null values, e.g., 94 and 96, are used to establishthat the desired mode has been stabilized, i.e. that the undesiredevanescent modes are dampened over the distance or length used for theapplicator 18. Lengths substantially less than one wavelength are notsufficient to accomplish the desired mode selection.

Furthermore, the specific absorption rate (SAR) produced at variousdepths in a bilayer phantom comprised of 1 cm of simulated fat and 10 cmof simulated muscle is improved as the guide wavelength is adjusted forthe critical value. This feature is related to, but different from, theuniformity of transverse heating.

For example, at a given thickness of dielectric material 28 shaped as ataper in the feed region and uniform in the load region, the SARs aresignificantly lower than those produced by the same thickness in fulllength as shown in Table I.

                  TABLE I                                                         ______________________________________                                        GUIDE HALF-                                                                   WAVELENGTHS T.sub.1   T.sub.2   T.sub.3                                       ______________________________________                                        238 mm       77 mW/g  28 mW/g   10 mW/g                                                                              tapered                                212 mm      111 mW/g  40 mW/g   14 mW/g                                                                              1.062"                                 160 mm      116 mW/g  50 mW/g   16 mW/g                                                                              +3/16"                                 ______________________________________                                         Notes:                                                                        All measurements are distance to node #3 minus distance to node #2 in 24"     test fixture with electric field feed.                                        Location T1 was 12 mm below the fatmuscle interface. This distance is         nearly 1/e depth; thus, the SAR at the interface is ca. 2.7 times higher      or 208 mW/g for the longest guide wavelength and 313 mW/g for the near        optimal guide wavelength. Since the net power was 50 W in all cases, the      efficiency of the applicator is about 4 mW/g/Watt for the longest guide       wavelength and about 6 mW/g/Watt for the near optimal case. This is a 50%     increase in efficiency.                                                       Lastly, the three sites of temperature measurement are 10 mm apart. In th     case of the longest guide wavelength, the second site is 36% of the first     site and the third site is 35% of the second site. In the case of the nea     optimal guide wavelength, the second site is 43% of the first site and th     third site is 32% of the second site. This implies that the rate of           attenuation with depth of propagation is improved with the near optimal       guide wavelength for the bilayer fat/muscle model studied here.          

The guide wavelength is adjusted by the use of low loss shims 41 tospace the dielectric material 28 away from the wall until the criticalguide wavelength is established and the SARs increase. The shims 41 mustbe thin because although the fields are low near the wall, excessivespace prevents stable null-to-null distances.

In FIGS. 12 and 13 the supply ducts 100 and 102 are waveguide belowcut-off with attenuation of 60 dB at the frequency of operation. Theyare connected by flexible hose 106 to a remote fan and source of air ata temperature not higher than 23 degrees C. FIGS. 12 and 13 demonstratethe method and apparatus for air cooling while maintaining contact withthe patient and the means for supression of RF leakage by the use ofwaveguide below cut off for cooling gas supply and return ducts.

The return duct 104 and 110 are also wave guide below cut-off andconnected to the low pressure side of the fan by flexible hose 108. Thesupply ducts 100 and 102 are located on one side to leave room forattachment of the applicator to a positioner. The air flow sensor(s) 112is used to interupt the power source via fault control 122 in order tonot overheat the skin and superficial subcutaneous tissues in the eventof fan failure.

FIG. 14 shows a system for detection of the individual therapeuticresponse and for treatment control. The method is based on change in thewave impedance of muscle as its blood flow and blood content increase.The change in wave impedance of the muscle is detected by a change inthe self impedance of the applicator measured at the terminals of theantenna, or at an integral number of half wavelengths from it, by meansof a reflectometer and complex ratiometer. The onset of muscle bloodflow is detected by a phase shift in applicator terminal impedance(toward the source) preceded by an increase of the reflectioncoefficient as the heating takes place.

The power source 114 is selected for frequency stability (1 part/1000drift) and sufficient power output to produce SARs between 150 and 250mW/g in bilayer fat/muscle phantoms using the applicator 18. Based onmeasurements in phantoms and human studies, 30 to 50 watts of CW powerare needed. The power source is protected by a three port circulator 116with a load to protect the power source should the applicator beoperated when not matched to or in contact with the patient. Thecirculator output is connected to the main line of a dual directionalcoupler 118. The main line continues to a tuner 120, comprised of a stuband a line stretcher then to the applicator/sensor 18. The air flowsensor 112, detects loss of air flow 111 to the applicator/sensor 18,and activates a fault control 122 to interupt the power source.

The forward and reverse coupled arms are connected to separate powerdividers 124 and 126. Attenuation to power levels appropriate for thesubsequent instrumentation is accomplished by separate attenuators 128and 130. When divided, the forward coupled arm enters a bolometer mount,or other power sensor, to measure the forward power via the meter 132.

The other half becomes the reference signal for a complex ratiometer134. The reverse coupled arm after power division is sampled by thereverse power meter 136 and becomes the test channel for the complexratiometer 134. The forward and reverse powers, 132 and 136, aresubtracted in the differential amplifier 138 and displayed by thedosimeter 140 as the net absorbed energy per unit time. Failure tomaintain the selected net absorbed energy per unit time also activatesthe fault control 122 to interupt the power source. Net absorbed poweris used, therefore, for three purposes: (1) to assist regulation of thenet energy per unit time delivered to the patient; (2) to establish avery good match to the patient at the baseline power level; and (3) todetect coupling faults.

Tests have shown that a return loss of 30 dB or better is advantageous.Similarly, the directivity of the reflectometer tuner 120 should be 40dB or better. The tuner 120 is adjusted to maximize the ratio of forwardto reverse power by a procedure well known to those skilled in the art.The complex ratiometer produces two output signals as functions of timeas shown in FIG. 15, the magnitude 142 and phase 144 of power wavescattering parameter S₁₁.

With reference to FIG. 14, if another form of heating is used, such asultrasound, the sensor functions may still be implemented. The changesin the instrumentation block diagram are to replace the high powergenerator 114, with a low power source at the same frequency, and toreduce the value of attenuation in attenuators 128 and 130 to beappropriate for the complex ratiometer 134 input levels. For example,the high power source of 30 to 50 watts would be reduced by 30 dB andthe attenuators 128 and 130 would be changed for 30 dB less attenuationin order to set proper signal levels at the complex ratiometer 134.

With reference to the complex ratiometer outputs shown in FIG. 15, thetime course of the complex scattering parameter discloses biophysicalevents in the muscle by virtue of the effect of changes in the waveimpedance due to the blood flow and blow content of that tissue. Sincethe applicator/sensor 18 is closely coupled to the tissue being heated,the self impedance of the applicator is effected by the change in waveimpedance in the tissue as the blood flow and blood content increase.

The change in applicator/sensor self impedance is monitored at theantenna's terminals, or at an integral number of half wavelengths towardthe generator, by changes in the complex reflection coefficient asnormalized by the forward wave.

Furthermore, in reference to the complex ratiometer outputs 142 and 144shown in FIGS. 14 and 15, the observed changes in the magnitude of S₁₁recorded over time in as 142 are a gradual increase in the magnitude,without a significant change in phase, as the tissues heat. These eventsare illustrated at time reference 146 when the specified net energy perunit time is first established. The latency, time at 148 minus time at146, to onset of phase shift 144 is shown in rectangular coordinates.The end of power application is shown at 150 and start of the range ofmotion/strength exercises during the cool-down period at 152 is alsoshown in FIG. 15.

In terms of a polar display of S₁₁, the magnitude increasessubstantially along a radius of constant phase. As the change ofmagnitude approaches a plateau, a latency of several minutes, shown at146 and 148, is required before the phase rotates toward the generatoron the Smith chart.

This phase rotation often takes place coincident with a reduction in thesubjective feeling of deep heat. This sequence of events takes typically10 to 20 minutes at the stated reference SARs. The latency, time at 148minus time at 146, corresponds to the time necessary to elevate muscletemperatures to the point where local vasodilation takes place. At thatpoint, the phase rotation takes place with characteristically smalladditional changes in magnitude.

Whereas certain specific embodiments of the improved method andapparatus for deep heat treatment of musculoskeletal disorders have beendisclosed in the foregoing description, it will be understood thatvarious modifications within the scope of the invention may occur tothose skilled in the art.

Therefore, it is intended that adaptations and modifications should becomprehended within the meaning and range of functional equivalents ofthe preferred embodiments. For example, changes in material anddimensions that are subsumed in the teaching of the instant patent maybe used in place.

Likewise the display options for detection of the therapeutic responsemay use any of the equivalent parameters of impedance, reflectioncoefficient, scattering parameter S₁₁, or admittance displayed inrectangular or equivalent polar co-ordinates or co-ordinatetransformations such as the Smith chart or Carter chart.

Similarly broader bandwidth (10% to 20%) impedance matching may beemployed to augment the narrowband reactive tuner as is well known tothose skilled in the art.

What is claimed is:
 1. Deep heat treatment musculoskeletal apparatus fordetection of therapeutic response and for treatment control based uponchange in the wave impedance of tissue as tissue blood flow and bloodcontent change comprising a power source, a combined radio-frequencywaveguide applicator and sensor operatively connected to said powersource and adapted for close coupling to tissue being heated, a dualdirectional coupler coupled to said power source and to said combinedradio-frequency waveguide applicator and sensor, and means operativelyconnected to said dual directional coupler for indicating a complexscattering parameter resulting from changes in wave impedance due toblood flow and blood content of the tissue being heated.
 2. The deepheat treatment musculoskeletal apparatus of claim 1 wherein said meansfor indicating a complex scattering parameter comprises a complexratiometer.
 3. The deep heat treatment musculoskeletal apparatus ofclaim 2 wherein said combined waveguide applicator and sensor has awaveguide with a waveguide wavelength and includes means associated withsaid waveguide for adjusting said waveguide wavelength.
 4. The deep heattreatment musculoskeletal apparatus of claim 3 wherein said waveguidehas a waveguide wall and said adjusting means comprises dielectric shimslocated adjacent to said waveguide wall.
 5. The deep heat treatmentmusculoskeletal apparatus of claim 2 wherein said combined waveguideapplicator and sensor has an exterior end portion and includes a highthermal conductivity material radome on said exterior end portion. 6.The deep heat treatment musculoskeletal apparatus of claim 5 whereinsaid combined waveguide applicator and sensor further comprise coolingmeans associated with said radome for cooling said radome.
 7. A methodfor deep heat treatment of musculoskeletal disorders of a personcomprising: providing deep heat treatment musculoskeletal apparatushaving a power source, combined radio-frequency waveguide applicator andsensor, a dual directional coupler and means for indicating a complexscattering parameter; providing a test fixture for use with the combinedwaveguide applicator and sensor; using said deep heat treatmentmusculoskeletal apparatus to induce deep heat treatment to themusculoskeletal part of a person and to detect a therapeutic response ofsaid person to the deep heat treatment by indicating a complexscatteriang parameter resulting from changes in wave impedance due toblood flow and blood content of the tissue being heated; optimizing saidtherapeutic response by establishing a critical waveguide wavelength;and verifying said critical waveguide wavelength through the use of saidtest fixture.